Wireless communications seems ubiquitous, with wireless internet, cellular telephones, pagers, and other wireless devices in common use. Most wireless communications networks use a specific system architecture optimized for the particular application being provided. For example, cellular telephone systems have many design aspects optimized to provide low power consumption and enable mobility for the handset. Cellular telephone systems typically operate in frequency-division duplex mode and use relatively low data rates. In contrast, cordless telephone systems, because of the short range operation and frequent battery re-charging, typically use higher burst data rates and operate in time-division duplex mode.
With increased integration levels and price reductions for electronics, many wireless devices are now being developed that can operate within different networks. One area of research and development is so-called “software radios” which are an attempt to provide highly flexible radios that can operate using a multitude of different waveforms and communications parameters. Software radio technology is a building block technology for multi-network operation, as the software radio can change operating parameters (e.g., modulation format or symbol rate) to match the network it wishes to communicate with.
As communications devices become capable of operating in different network types, the problem of discovering and entering into communication with a network becomes more complex. Entering a network is typically straightforward for a device designed for single-network operation, as the device is generally preprogrammed to use signaling parameters compatible with the network. In contrast, devices designed for multi-network operation are faced with the challenge of determining appropriate signaling parameters to allow communication with the network.
While differences in data rates and modulation formats can be handled by establishing fall-back data rates and modulation modes to provide compatibility, other system design aspects prove more difficult. For example, a time-division duplex (TDD) system uses a common frequency for transmission in both directions (e.g. from a base station to a handset and vice versa). In contrast, a frequency-division duplex (FDD) system uses different frequencies in each direction (e.g., a forward link carrier frequency for transmission from the base station to the handset and a return link carrier frequency for transmission from the handset to the base station). Accordingly, providing communication between a device using one duplex mode and a network using the other duplex mode is not normally possible.
Heretofore, most systems have operated in only one or the other type of duplex mode, and switching between modes is not generally done. While some terminals capable of switching modes are known, these terminals usually know a priori which type of network they are attempting to enter. When a network can be operating in either mode, the mode of operation of the network is unknown, or terminals of incompatible types wish to enter a network (e.g., a TDD terminal into an FDD network, or vice versa), several difficulties are presented.